The present invention relates generally to the field of nuclear reactors, and, more particularly, to an improved method of making a neutron-absorbing material for use in such reactors and the improved material produced by this method.
It has long been known that certain elements, such as boron, have a capability of absorbing thermal neutrons. These neutron-absorbing elements are commonly used in the control rods of a nuclear reactor, which may be selectively lowered into the reactor core to slow down the reaction. Some types of reactors have a hopper of "shut-down" balls or pellets positioned overhead the core such that, in the event of an emergency, the balls may be released into the core to slow down the reaction.
Heretofore, such "shut-down" balls have been manufactured by hot-pressing, extruding or otherwise bonding boron carbide (B.sub.4 C) and graphite (C) together. While containing the desired quantities of elemental boron, such prior art "shut-down" balls proved to have a number of disadvantages. Specifically, these disadvantages included a low abrasion resistance, as manifested by a tendency to dust or chalk (and thus allow uncontrolled and unrecoverable release of the neutron-absorbing material into various areas of the reactor), a tendency to oxidize, and were susceptible of severe erosion when subjected to heated water vapor rising upward from the reactor core. Further details as to such prior art control materials and the uses therefor may be found in one of the followig U.S. Pat. Nos.: 3,088,903, 3,108,886, 3,146,281, 3,403, 008, 3,565,762, 3,769,160, 3,914,371, 4,076,583, 4,213,883, and 4,474,728.